The practice of measuring end-tidal carbon dioxide during the administration of anesthesia, particularly regional anesthesia, has grown markedly in the past several years. The reasons that anaesthesiologists have embraced this technique are described more fully in U.S. Pat. No. 5,335,656 which is incorporated herein by reference in its entirety.
The preferred nasal cannula used in this procedure is a cannula which insufflates the patient with oxygen through one nare of a cannula and separately samples the exhaled gases by drawing the exhaled gas from the other nare into a conventional carbon dioxide analyzer. The cannula is preferably provided with an internal wall, a partition, a barrier or a system in the face piece to keep the conduits completely separate from one another for insufflation and sampling, however, separate lines can be used or even multiple nares for insufflation and sampling, though the latter device substantially increases the risk of gases mixing which can distort the readings for end-tidal carbon dioxide. It is preferred that two nares only are employed and that each nare performs only one function, i.e., insufflation or sampling into or from separate nostrils, detecting pressure or breathing characteristics, etc. Likewise, insufflation has normally been continuous, however, it could advantageously be intermittent which would further improve the end-tidal carbon dioxide measurement by insuring that gases being sampled where representative of exhaled gases undiluted by the other gases being insufflated. Most preferably, the intermittent insufflation is accomplished by the apparatus and method described in U.S. Pat. No. 5,626,131 which is incorporated herein by reference in its entirety. Other so-called demand insufflation devices which being insufflation upon the start of inhalation can also be employed.
Normal nasal cannulae are designed with the nares having a slight inward curvature as the nares extend upward from the face piece. This is anatomically desirable and important for imparting the proper direction of the insufflating gas into the nasal cavities, receiving the sampled gas(es) from the patient, detecting pressure or breathing characteristics of the patient, etc. When the patient is in the upright sitting position or ambulatory, this is the most satisfactory design configuration. Conversely, problems can be encountered if the patient is horizontal or prone and tends to accumulate secretions in the nasal cavities. It can be a particularly vexing problem if either the insufflation or sampling nare becomes occluded during the use of the cannula for sampling, monitoring end-tidal carbon dioxide during the administration of anesthesia, detecting pressure or breathing characteristics of a patient, etc.
One problem which can readily occur during use of a cannular positioned in the nostrils of a patient is that the primary opening, formed in the remote end wall or surface, of one or both of the nares may become either partially or fully occluded, blocked, clogged or otherwise obstructed by, for example, mucosal secretions and/or soft mucosal tissue during use of the nasal cannula. This is particularly true if the nasal cannula is used in a patient for an extended period of time, e.g., for a few hours to eight or more hours during a sleep diagnostic session. Over the course of time, the mucosal secretions and/or soft mucosal tissue, as well as any inhaled particulate matter which may collect within the nostrils, can either partially or completely occlude, block, clog or otherwise obstruct the primary inlet/outlet opening to one or both nares and such occlusion, blockage, or obstruction can then prevent that nare from properly achieving its intended function, e.g., prevent or seriously inhibit the nare from properly supplying the desired gas to the nostril of the patient, withdrawing or sampling the desired sample from the nostril (e.g., sampling end tidal CO2 in the exhaled gases of a patient), monitoring breathing characteristics of a patient (such as respiratory air waves and air flow), or detecting changes in pressure within the nostril during patient breathing.